Power supply for a stepping motor

ABSTRACT

A programmed power supply rectifies multi-phase A.C. power to produce signal polarity D.C. voltage and applies the D.C. voltage to the stator windings of a multi-phase motor in a predetermined sequence so as to develop a rotating magnetic field, and the motor responds thereto by rotating discrete mechanical increments in a step-by-step fashion. The stator windings are arranged in a star configuration having a neutral and each winding is energizable independently of the others. The power supply includes a triggerable rectifying element for each winding and a programmer which is responsive to an external source of signals for triggering the rectifying elements in the predetermined sequence.

United States Patent 1151 3,706,924 Adler 1451 Dec. 19, 1972 [5 1 POWERSUPPLY FOR A STEPPING 3,355,646 11/1967 0616 ..3l8/685 MOTOR 3,437,8994/1969 Hirokawa.... 318/696 3,385,984 5/1968 O'Re an ....3l8/696 [72]lnvenm" (305 Mesa Callf- 3,535,604 10/1970 Madsgn et al. ..3l8/696 [7 3]Assignee: Royal Industries, lnc., Pasadena,

Calm Primary Examiner-G. R. Simmons [22] Fl d D 4 1969Attorney-Christie, Parker& Hale 1e ec.

21 Appl. No.: 882,035 [57] ABSTRACT A programmed power supply rectifiesmulti-phase A.C. power to produce signal polarity D.C. voltage c(Ell.38/625653; and applies the DC. voltage to the stator windings of a multiphase motor in a predetermined sequence so [58] Fleld of Search 318/138,696 as to develop a rotating magnetic field, and the motor 310/49responds thereto by rotating discrete mechanical increments in astep-by-step fashion. The stator [56] References C'ted windings arearranged in a star configuration having a UNITED STATES PATENTS neutraland each winding is energizable independently of the others. The powersupply includes a triggerable 3,297,927 1/1967 Blakeslee et al ..3l8/138rectifying element for each winding and a programmer 3, ,19 6/ 70 Goto-.3l8/696 which is responsive to an external source of signals for13,23,223 13/132: :mlith triggering the rectifying elements in thepredetermined O a OIOWICZ e a e uence 3,445,741 5/1969 Gerber ..3l0/49 Xq 3,461,365 8/1969 Newland et al ..3 18/696 X 3 Claims, 4 DrawingFigures l l is g /b 7 (PMs/ 4mm /3 l i 1 est/2 w -I i l i /Z1 1; Mam/2wwflg i i w i /5 a J. l|, #040 L /6 J 9/6/1444 /L 6475 l 0431 @"A' A l lg 6 1 i i 1 I 1 g I l 1 I 1 i w I w M g l I A/EP6/Z4BLE 62L J [0/W/A/D/A/ES PATENTED DEC 19 |912 SHEET 1 0F 3 mmmm 3 706 924 SHEET 2 BF 3I llll III POWER SUPPLY FOR A STEPPING MOTOR This invention relates to apower supply and in particular an electronic power supply particularlyadapted for use with a control rod drive mechanism employed with anuclear reactor.

In a control rod drive mechanism for a nuclear reactor it is generallydesirable for positioning the control rod within the nuclear reactorvessel to generate a rotating magnetic field and then translate theresultant rotary mechanical motion to linear mechanical motion. Varioustypes of electrical drive motors have been employed for this purpose.The power supplies that have been employed for this purpose cangenerally be classified as three-phase sinusoidal or electronic gatingpower supplies. The three-phase sinusoidal power supplies includerotating machines, such as amplidyne systems or commutator inverter, andthe solid state cycle-converter. The amplidyne system inheres all of theproblems of rotating machinery in addition to being big and bulky. Thecommutator-inverter also inheres all of the disadvantages of rotatingmachinery. The cyclo-converter produces a direct current output of oneto three cycles per second along with a 180 cycle ripple that causesvibrations in the control mechanism leading to excessive wear. Theelectronic power supplies have been designed with triggerable elementstherein, such as silicon controlled rectifiers (SCRs). The problemassociated with the prior art type of gated power supplies is that theSCRs are highly subject to misfiring and cause subsequent loss ofcontrol of the motion of the control rod. This type of power supplyutilizes triggerable elements to energize the drive mechanism motor in apre-set sequence. This system requires voltage pulses to energize thetriggerable element and utilize the resulting change in voltage todeenergize another triggerable element, by use of a commutatingcapacitor. It has been found that external disturbances such as unwantedpulses generated by lightning, the plant switch gear or other sourcescan cause such prior art gated power supplies to misfire the triggerablecircuits thereby rendering the associated control drive mechanismsunreliable.

The present invention provides an improved electronic gated power supplyfor the production of a rotating magnetic field and one that produces arotating magnetic field having steps or increments of mechanical degreesrather than 30 as in the prior art when employed with a four-pole motor.The present invention affords, a triggerable power supply that istransient tolerant, has less vibration and is simpler than thethree-phase sinusoidal or the gated power supply employing a capacitorfor turning off the triggering element or SCR's. The present invention,furthermore, has been found to be reliably operative even thoughexternal disturbances such as those generated by lightning, plant switchgear and the like which render the prior art gated supplies unreliable.The reliability of the triggerable elements of the present invention isenhanced by employing alternating voltage to de-energize the elements.

The improved control over the rotating magnetic field is effected bysequencing the pulsing of the energizable windings of the drive motor ina 3-on, 2-on, 3- on, etc. sequence wherein three windings are energizedmomentarily, then one winding is de-energized and the other two remainenergized, etc., so as to electrically step around the energizablewindings until all of the windings have been energized in accordancewith this logic. With this action the motor rotor coupled to theenergizable windings for the motor will be stepped through the 15increments. In the prior art power supplies, three coils, no more noless, have to be energized at any one time for reliable operation and anincremental step of 30 mechanical degrees is produced. It will also benoted that because of the 3-3 sequence of the prior art power suppliesif more than three coils are energized the system may fail to operate.

From a method standpoint the present invention comprehends theproduction of a rotating magnetic field in a multi-phase windingincluding the steps of providing a direct current source for energizingeach of the multi-phase windings and controlling the direct currentsource to cause the windings to be energized in a step-like fashion forproducing the rotating magnetic field to effect mechanical increments of15 in a fourpole reluctance motor, for example. The logic for effectingsuch a magnetic field is to control the energizable windings of themotor in a 3-on, 2-on, 3-on logic in rotating sequence for generatingthe rotating magnetic field.

From an apparatus standpoint, the power supply of the present inventionis adapted for producing a rotating magnetic field in a motor having astator and a rotor. The stator having a plurality of independentlyenergizable windings employed for multi-phase operation. In one specificembodiment, the windings may be arranged in a star configuration for afour-pole, six-phase reluctance motor. A controllable direct currentsource is connected to each of said windings for independentlyenergizing and de-energizing the windings in a preselected sequence forgenerating the rotating magnetic field in the stator to cause the rotorto respond thereto. Control means are connected to the direct currentsource for controlling the energization and deenergization of saidwindings in the 3-on, 2on or 3-on, etc., logical sequence while steppingaround the star configuration in either a clockwise or acounterclockwise fashion depending upon the desired direction ofrotation. The direct current source may comprise a plurality oftriggerable elements such as the SCRs which are gated on by means of aprogrammer device for triggering them in accordance with theaforementioned logic. The SCRs are energizably controlled by a directcurrent triggering pulse and de-energized, by the alternating voltageapplied to their anode electrodes, when the negative half cycle of thealternating voltage is applicable. The precise control of the rotatingmagnetic field and thereby any mechanism controlled thereby is effectedthrough the provision of a programmer which sequentially controls theenergization of the triggerable elements. The programmer may be anyconventional type of programming device, electronic orelectromechanical, and in the disclosed embodiment takes the form of anencoding element having a coded disc. The coded disc has a controlpattern recorded thereon, and with the rotation of the encoder thepattern is sensed so that a series of signals are derived therefrom, inresponse to sensing the pattern on the disc, for triggering the SCR 9 inthe desired sequence. When used in the nuclear reactor the drive of theencoder is synchronized with the control rod mechanism motion.

These and other features of the present invention may be more fullyappreciated when considered in the light of the following specificationand drawings, in which:

FIG. 1 is a schematic-wiring diagram of the power supply embodying thepresent invention;

' FIG. 2 is a vector diagram of the electrical relation-' ship of theenergizable windings of FIG. 1 illustrating the productionof therotating magnetic field;

' FIG. 3 is a schematic wiring diagram of the power supply illustratedin FIG. 1; and

FIG. 4 is a plan view of the coded disc illustrated in FIG. 1.

' Now referring to the drawings, the power supply of a the presentinvention will be examined in more detail.

by those skilled in the art that the reluctancemotor is a more reliabletype of drive motor'but requiring a more complex power supply thansimilar drivemotors. The power supply of the present invention, however,could be employed with a'linear drive motor such as the mag-jac" motor.For this purpose the stator of the drive motor is illustrated asarranged in a six-phase star configuration. The energizable windings ofthe stator reading in a clockwise rotation are identified by thereference characters A, B, C, AA, BB, and CC. The energizable windingsare energized by direct current provided by the triggerable directcurrent source generally identified by the reference numeral 10. Thewindings are energized from the direct current sources in a sequentialfashion, either in a clockwise or counterclockwise direction dependingupon the desired direction of rotation for the motor rotor.

The direct current power source includes a plurality oftriggerableelements 1 1 that are gated to maintain them in conduction for apreselected interval and inaccordance with the desired sequence forenergizing the windings Athrough CC. The triggerable elements 11 may beconventional silicon controlled rectifiers (SCRs), having a controlelectrode connected to a gate of the elements 11. The gate drives 12 areconnected to a programmer 13 that provides a series of control signalsto the gate drives 12 that trigger the elements 11 in the correctsequence for generating the rotating magnetic field in the energizablewindings. For this purpose the programmer 13 is illustrated in the formof an encoder having an optical coding disc providing the signals to thegate drives 12. With this type of programmer the sequential gatingsignals are generated by means of a coded disc 14 mounted to therotating shaft 15 controlled from the program drive motor 16. The codeddisc 14 has the desired pattern of control segments recorded thereon interms of optical characteristics or light transmitting and opaquesegments. The optical coded disc 14 is associated with a light source 16for illuminating a section of the coded disc as it rotates thereby anddirects the light signals through the light transmitting segments of thecoded disc and onto the photosensor 17. With the impingement of thelight signals onto the photosensors 17 the optical pattern of the disc14 is reproduced as a corresponding pattern of electrical signalsprovided by the photosensors 17. The photosensors 17 are arranged withindividual amplifiers 18 for each track recorded on the coded disc 14.The output of the amplifiers 18 are coupled to the gate drives 12.

Before examining the detailed operation of the power supply 10, thesequence of energizing the windings A through CC will be discussed. Asmentioned hereinabove, the desired logic for energizing the starwindings is to effect the rotating magnetic field for producingmechanical steps of 15. For this purpose, the logic for sequentiallyenergizing the windings is a 3- on, 2-on, 3-on, etc., logic. Assumingfor the present that clockwise rotation is desired and that initiallythree windings are energized, namely, A, B and C, reference to thevector diagram of FIG. 2 will show the relative location of the vectorsrepresentative of the energization of windings A, B and C. The windingsA, B andC are arranged apart electrical degrees. When this electricalcondition prevails, then, the resultant vector will overlie the vectorfor winding B and have a magnitude or length extending beyond the vectorB, as illustrated. During the next succeeding interval, winding A isde-energized leaving only windings B and'Cenergized. Since the windingsB and C are electrically spaced apart by 60, the resulting vector willlie between these two vectors and therefore will shift 30 from theposition overlying vector B to the position illustrated in FIG. 2displaced 30 between vectors B and C. During the nextsucceeding'interval, windings B, C and AA are energized so that theresultant vector is again shifted a further 30. This third resultantvector will overlie the vector C, as illustrated. This same shifting ofthe resultant vector will prevail as the windings are energized with the3-on, 2-on logic, etc., thereby defining the rotating magnetic field.Inthe generation of such a rotating magnetic field in the four-pole,sixphase reluctance motor, the sequence of energization of the windingsis effected in twelve electrical steps to effect the complete traversalof the windings from the assumed initial condition wherein the windingsA, B and C are energized to the point where the three same windings arere-energized. In such a motor, this magnetic action produces steps of 15mechanical degrees. Under these conditions, the energization of thewindings in the twelve steps is illustrated in the Chart I below:

At this point it should be noted that the programmer 13 will provide thenecessary signals for actuating the triggerable elements 11 in thecorrect sequence to effect the energization and de-energization of thewindings as noted in Chart I.

When the programmer 13 is in the form of an encoder having a coded disc14 with the light transmitting segments coded thereonfor providing thedesired electrical signals it may take the form of the patternillustrated in FIG. 4. The coded disc 14 is illustrated in FIG.

4 as having six tracks that are identified as tracks A, B, C CC tocorrespond with the identification of the energizable windings. Theouter track illustrated in FIG. 4 is not employed for the present butwill be described hereinafter. As will be appreciated from examiningChart I, each optical segment has an arc corresponding to five units oflength and each track is disdisplaced two units from the 0 position andthen extends from position 2" a distance of five units, while thepattern in track C is displaced two units from track B, etc. It will benoted that the pattern illustrated in FIG. 4 is symmetrical on each halfof the disc 14 and may be employed for producing a second seriesofcontrol segments as will be disclosed hereinafter. It should be notedthat the photosensors 17 are diagrammatically positioned on the disc 14in FIG. 4 for sensing the six tracks. For this purpose, the sensors 17are arranged in radial alignment on the encoding element 14 forintercepting the light rays transmitted through the tracks and providingthe corresponding electrical signals reproducing the pattern on theencoding disc 14 for effecting the desired triggering action on thetriggerable elements 11. 1

Referring now to the outer track on the disc 14, the purpose of thistrack will be explained. The purpose of this outer track H is to placethe control rod drive motors in the two windings energized conditionwhenever the drive motor is commanded to stop. For this purpose, thisouter track is provided with segments H2 spaced apart on the disc andlocated to correspond to the segments when two coils are energized. Thistrack is sensed by a sensor 17H to provide a hold control signal tocontrol the program drive motor 16 to move the disc 14 to a positiondefined by the segments H2 to cause only two motor coils to be energizedin the hold position; see FIG. 1. This results in a large power savingsand heat reduction in the drive apparatus since at any one time amajority of drives are maintained in the hold condition. in applicationswhere these factors are not important, the outer track function can beeliminated.

With the above description in mind, then, a detailed description of theoperation of the circuits of FIG. 3 is in order. The signals generatedfrom the programmer 13 will be assumed to be generated from the encodingdisc 14 as the result of the actuation of the drive motor 16, a halfrevolution of the disc generating the complete cycle of the magneticfield. The signals will be derived from the programming means 13 forgating the elements 11 in the sequence of steps shown in Chart I.Initially, then, the gating signals are derived from the programmer 13for driving gates A, B and C, etc. of the gate drives 12. The gatedrives 12 comprise a plurality of individual gate drives identified bythe letters A, B, etc. to correspond with the identified stator windingsof the drive motor. The gate drives 12 are coupled to control thetriggerable elements 11. The triggerable elements 11 for each phase ofthe drive motor are illustrated in FIG. 3 as comprising six triggerableelements or SCRs for each phase. Each group of six elements 11 are shownwithin a block, with the blocks identified M1, M2 M6. The signals fromthe gating drives 12 are coupled to the gate electrode of each element11 for controlling the time that the element is energized. Each anodeelectrode for each group of the elements 11 is connected to analternating current source, as illustrated. The cathode electrodes areconnected in parallel circuit relationship to an individual winding,such as the winding A, to provide the necessary energization of thewindings. Each of the six cathode electrodes of the elements 11 thatcorrespond to the same windings are connected'in common for energizingthe winding. Tracing a specific circuit from the programmer 13 it willbe seen that the control signal from the programmer for winding A isapplied to the gating drive A by means of the lead wire 20. The outputfrom the gating drive A is applied by means of the lead wire 21 to eachof the triggerable elements within the block M1. With the gating signalapplied to the elements during the interval that the alternating currentat each anode electrode is in the positive halfcycle, the correspondingelement will conduct until the negative half-cycle is reached. With theconduction of these six elements the output currents therefrom may becombined into a bus similar to the one identified as the A bus directlyconnected to the A winding. In the same fashion the gating signals maybe traced from the programmer 13 to the controllable elementsll for eachof the other windings. For example, the control segment from theprogrammer 13 for gate drive CC is applied thereto by means of the leadwire 25 and the output from the gate drive CC is coupled to the elements11- by means of the lead wire 26. The lead wire 26 is connected to thegate electrode of each of the elements 11 that are further identified asthe CC elements. As in the case of the A elements, the output currentsare derived from the cathode electrodes of the CC elements that areconnected in parallel by means of the lead wire 27 and to the CC buswhich is connected to the CC winding of the drive motor. Each of theother segments may be similarly traced and are shown connected in theircorrect relationship to the triggerable elements for each phase Ml M6 inFIG. 3. It should be recognized that the gating signals are onlyeffective for triggering the elements 11 to a conductive condition andthat with the alternating voltage applied to the anode electrode, in thenegative one-half cycle, each triggered element will be renderednonconductive until the anode voltage again becomes positive. Thisconducting condition exists as long as the triggering signal is receivedfrom the programming means 13.

It should now be evident that with the above structure in mind therotating magnetic field is produced through the sequential energizationof the windings A-CC in the 3-on, 2-on, etc., logic. Then the controlsignals are applied to the program drive motor 16, by means of theoperator in the nuclear reactor application, the shaft 15 and the codeddisc 14 are rotated.

With the sensing of the coded disc 14 the series of gating signals toeffect the 3-on, 2-on logic is generated and applied to each of thegating drives A, B, C, etc., for triggering the six elements 11 of eachphase to effect the energization of the windings A CC in accordance withthe twelve steps illustrated in Chart 1 in one half revolution of theencoding disc 14. A further advantage of the above logic may be realizedwhen such a power supply is employed for energizing a reluctance motorutilized to control the control rod in a nuclear reactor. it will beappreciated that the control for such a reactor must be accuratelycontrolled and the misfiring of the elements 11 must be minimized aswell as the reliable energization maximized. For this purpose thepresent power supply lends itself to redundant operation since a similarpower supply may be arranged in parallel circuit relationship with thepower supply for energizing the windings in a redundant fashion. Forthis purposethe programmer 13 may take the same form as the encodingelement 14 due to the redundancy of the pattern employed on the encodingarranged in parallel circuit relationship with thoseof the primarysupply 10 so that if there is a malfunction in the power supply 10 andnot in the auxiliary power supply, the windings A through CC will beenergized in the correct sequence. It should be recognized that thecircuit of the present invention allows for redundant operationcompletely through to the motor windings. This type of redundancy, tothe motor windings, is not possible with other known power suppliesparticularly for nuclear reactor control drives.

What is claimed is:

1. A power supply for producing a rotating magnetic field in a steppingmotor stator comprising:

a stepping motor having a stator and a rotor, the stator having aplurality of independently energizable windings arranged in a starconfiguration with each winding connected to a neutral,

a single polarity direct current source connectable for independentlyenergizing each of said windings and operative when connected to awinding to supply current through the winding and the neutral, saidsource having an individual triggerable rectifying element for each ofsaid windings, each of said triggerable elements comprising a pluralityof groups of silicon controlled rectifiers each having first, second andthird electrodes, the first electrodes of each individual group ofrectifiers being connected in common for accepting a gating controlsignal for rendering the rectifiers conductive, the second electrodes ofeach group of rectifiers being independently connectable to analternating current power source and the third electrodes of each groupof rectifiers being connected in common to a corresponding winding forsupplying the direct current to the winding upon' condu tion of therectifier, a multl-p ase a ternatmg current source having each phaseindependently connected to one of the second electrodes in each group ofrectifying elements, controllable means for independently supplyinggating control signals to the first electrodes of each group ofrectifying elements, and g program means constructed and defined forcontrolling the controllable means to supply the gating control signalsto the first electrodes within each rectifying element group in apreselected sequence in accordance with the selected program andindependent of the position of the motor rotor so as to cause theenergization and de-energization of the multi-phase windings in astep-by-stepfashion and thereby to cause the generation of a rotatingmagneticfield for producing the'rotation of the rotor in 15 mechanicaldegreeincrements, the application of a gating control signal to saidfirst electrodes of each group of rectifying elements causing theconduction of said rectifying elements upon the substantiallysimultaneous occurrence of the positive half cycles of the alternatingcurrent voltage applied to said second electrodes of said rectifyingelements from said alternating current source while the occurrence ofthe negative half cycles of the alternating current voltage applied tosaid second electrodes maintain the rectifying elements non-conductiveand/or render the rectifying elements non-conductive, whereby anyexternal disturbances causing a non-conductive element to be triggeredto a conductive condition not in accordance with the selected programwill be conductive only for the remaining duration of the positive halfcycle of the alternating current.

2. The power supply as defined in claim 1 wherein the multi-phasewindings are arranged in a six-phase star configuration and thecontrollable means responds to the program means to supply the gatingcontrol signals in a 3-2-3, etc. sequence.

3. A power supply as defined in claim 1 wherein the program meanscomprises a disc having a code pattern recorded thereon for effectingthe desired energization of said rectifying elements in said sequence.

Po-ww UNITED STATES PATENT. OFFICE g 569 CERTIFICATE oI CORREC'HGNPatent No. 3,706,924 Dated December 19. 1972 Inventor-(3) 7 Jason A,Adler It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Col. 2, line 39, reads "20m", should read --2 -on-.

Col. 3, line 43, reads "gate of the elements 11." and should read -ga.te drive 1i for providing a triggering signal to the gate electrode ofthe elements 1l.-

Signed and sealed this 20th da of November 1973.

(SEAL) Attest:

EDWARD M.FLETCH'ER,IJR. I RENE TEGTMEYER Acting Commissioner of PatentsAttesting Officer Po-ww UNITED STATES PATENT. GEFECE @ERTIFICATE @FCQRECTEN Patent No. 3 706, 924 Dated December 19.. 1972 lnventofl JasonA, Adler It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 39, reads "2on',', should read --2 -on-. Col. 3, line 43,reads "gate of the elements- 1 1." and should read "gate drive 1i forproviding a triggering signal to the gate electrode of the elementsll.--

Signed md sealed this 20th day of November 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D, TEGTMEYER Attestlng Offlcer A tingCommissioner of Patents

1. A power supply for producing a rotating magnetic field in a steppingmotor stator comprising: a stepping motor having a stator and a rotor,the stator having a plurality of independently energizable windingsarranged in a star configuration with each winding connected to aneutral, a single polarity direct current source connectable forindependently energizing each of said windings and operative whenconnected to a winding to supply current through the winding and theneutral, said source having an individual triggerable rectifying elementfor each of said windings, each of said triggerable elements comprisinga plurality of groups of silicon controlled rectifiers each havingfirst, second and third electrodes, the first electrodes of eachindividual group of rectifiers being connected in common for accepting agating control signal for rendering the rectifiers conductive, thesecond electrodes of each group of rectifiers being independentlyconnectable to an alternating current power source and the thirdelectrodes of each group of rectifiers being connected in common to acorresponding winding for supplying the direct current to the windingupon conduction of the rectifier, a multi-phase alternating currentsource having each phase independently connected to one of the secondelectrodes in each group of rectifying elements, controllable means forindependently supplying gating control signals to the first electrodesof each group of rectifying elements, and program means constructed anddefined for controlling the controllable means to supply the gatingcontrol signals to the first electrodes within each rectifying elementgroup in a preselected sequence in accordance with the selected programand independent of the position of the motor rotor so as to cause theenergization and de-energization of the multi-phase windings in astep-by-step fashion and thereby to cause the generation of a rotatingmagnetic field for producing the rotation of the rotor in 15 mechanicaldegree increments, the application of a gating control signal to saidfirst electrodes of each group of rectifying elements causing theconduction of said rectifying elements upon the substantiallysimultaneous occurrence of the positive half cycles of the alternatingcurrent voltage applied to said second electrodes of said rectifyingelements from said alternating current source while the occurrence ofthe negative half cycles of the alternating current voltage applied tosaid second electrodes maintain the rectifying elements non-conductiveand/or render the rectifying elements non-conductive, whereby anyexternal disturbances causing a non-conductive element to be triggeredto a conductive condition not in accordance with the selected programwill be conductive only for the remaining duration of the positive halfcycle of the alternating current.
 2. The power supply as defined inclaim 1 wherein the multi-phase windings are arranged in a six-phasestar configuration and the controllable means responds to the programmeans to supply the gating control signals in a 3-2-3, etc. sequence. 3.A power supply as defined in claim 1 wherein the program means comprisesa disc having a code pattern recorded thereon for effecting the desiredenergization of said rectifying elements in said sequence.